Magnetic tape recording/playback systems are subject to degradation by the accumulation of debris on the magnetic transducer head, and must be periodically cleaned. This can require the interruption of normal processing (of a stream of data for a digital computer memory storage device, for example) and user intervention. This invention integrates cleaning means in the form of a section of abrasive tape used for a leader at the end of the medium. A recording/playback mechanism can respond to an increase in error rate by automatically moving to the end of the recording medium, employing the cleaning tape/leader as needed, and resuming the recording or playback process without the need for manual intervention.
One prior art technique used a separate "cleaning cartridge" to perform the necessary maintenance on the recording transducer. The recording/playback process must be stopped, the data cartridge removed, and the cleaning cartridge inserted. When cleaning is complete, the cleaning cartridge must be removed and the data cartridge reinserted. Only after these two operations can the recording/playback process be resumed. In order to automate the process, an autochanger mechanism or tape library can have one or more cleaning cartridges in its storage magazine(s). This reduces the impact of the cartridge swaps, but two cartridge swaps are still required to perform the cleaning operation.
A problem with cleaning tape designed for routine cleaning is that if excessive tape head wear is to be avoided, the cleaning tape is only partially effective. If the cleaning tape is made sufficiently effective to thoroughly remove debris from the read/write heads, then a routine must be established for using the cleaning tape only when necessary.
In the use of magnetic tape for storage of computer data, errors, even infrequent in occurrence, represent a significant problem. In some applications, loss of analog or digital data must be significant before the equipment becomes unusable. The user is able to perform a cleaning operation in response to recognized dropout errors but does not immediately lose the ability to use the equipment prior to cleaning. In contrast, the loss of a single bit of computer data can be of significant import and recovery from each error must be done in a manner that ensures error-free data storage and retrieval. While error correction is possible, data loss can still present problems.
Existing linear and helical scan tape drives that are used for storage and retrieval of computer data make use of a single reel magnetic tape cartridge to house the magnetic tape media. This media format uses a special leader or leader block attached to one end of the magnetic tape to enable the tape drive to extract the magnetic tape from the magnetic tape cartridge.
"Leader tape" constructed of thicker, stronger tape is sometimes used between the tape that forms the magnetic storage medium, and the hub reel. Leader tape has performed various functions, including identification, timing and an ability to resist wear. Leader tape can be located at any location on the tape, although it is usually at the ends of a reel of tape. The leader can be at either end of the reel, so that "leader tape" can be at the trailing end of a supply reel. Such tape located at the end of a reel may be referred to as "trailer tape." For the purposes of this document, "leader tape" will be used to refer to the type of tape, rather than its location, and therefore should include "trailer tape."
"Tape recorder" is intended to mean magnetic tape transcription equipment. This includes standard tape recorders with fixed or movable heads, as well as arcuate scan and helical scan tape transcription equipment used in analog and digital tape recorders. In the preferred embodiment, a linear transcription heads is employed, although the invention has application in other tape recording environments. "Transcription" is intended to mean read and/or write operations of the tape recorder, and is not intended to be limited to a particular use for the data.
Prior art music cassette tapes have included special material on leader tape. Such leader tapes were designed to be crossed at each beginning sequence of operating the tape. If the leader tape had an abrasive cleaner of sufficient strength for cleaning the tape head when such cleaning is necessary, then the leader tape would tend to cause undue wear of the tape heads. That is because each use of the tape from the end would result in such abrasive cleaning. Therefore, end of tape leaders had a limitation in that it was necessary that the cleaning effectiveness be reduced so that excess wear would not result from the use of such tapes.
Under ideal circumstances, a mildly abrasive cleaning tape should be run across the tape head at intervals as determined by the need for cleaning the tape head. This determination can be made manually or by detecting recording characteristics.